1. Field of the Invention
The present invention relates to a method of carrying out chemical reactions, other than alkylations of aromatic compounds, in a reaction distillation column on an acid catalyst. The present invention also relates to apparatus comprising reaction distillation columns suitable for use in the present method.
2. Discussion of the Background
Reactions on catalysts in distillation columns are known. In such reactions, a separation by distillation of the reaction products takes place immediately after the reaction occurs.
In DE-A-39 30 515, shaped bodies of macroporous ion exchangers are employed in order to carry out various reactions, in particular the synthesis of methyl tertbutyl ether, in columns. The ion exchanger shaped bodies can also be doped with metals of subgroups 7 and 8 of the Periodic Table of the Elements.
According to EP-A-0 415 310, tertiary alcohols are prepared from isoolefins and water on acid cation exchanger resins in distillation columns.
However, ion exchanger resins are temperature-sensitive. Thus, they can only be employed for brief periods at temperatures of 150.degree. C. When using ion exchangers in long-term operation, on the other hand, temperatures of only up to about 110.degree. C. are utilized, which for some reactions leads to a greatly increased and economically uninteresting reaction time.
According to EP-B-0 008 860, methyl tert-butyl ether can be prepared in reaction distillation columns on acid ion exchangers in cloth bags of a cloth belt. In addition to the facts that ion exchangers are temperature-sensitive and the cloth bags can break open, in this case, the entire installation must be shut down when exchanging inactivated catalyst. In this case also, only an entire cloth belt can ever be exchanged. Thus, it is not possible to exchange small catalyst regions rapidly, and production must be interrupted for at least several hours to replace inactivated catalyst.
In EP-A-0 302 336, a process for cleaving alkyl tert-alkyl ethers is described. The catalysts used are preferably acid cation exchangers but acidic SiO.sub.2 or acidic Al.sub.2 O.sub.3 can also be used. However, the catalyst is arranged at the foot of the column, that is, in the liquid region. The arrangement corresponds to a kettle with an attached column. Accordingly, the reaction only takes place in the liquid phase. The catalyst is therefore not a distillation packing material in the gas-liquid region, and the catalyst does not have a rectifying distillation effect.
In DE-C-26 58 569, the preparation of shaped catalysts, chiefly containing TiO.sub.2, is described. TiO.sub.2 is prepared from metatitanic acid gel, extruded and then calcined at 200.degree. to 800.degree. C. The catalysts can be used for removing nitrogen oxides from gases or for the catalytic oxidation of butene to acetic acid in the gas phase. Reactions in a gas-liquid system are not described.
According to EP-B-0 189 683, aromatic compounds are alkylated in a reaction distillation column on a fixed bed having an acid catalytic distillation structure. In this case, in particular, acid cation exchanger resins and also acid molecular sieves of the type SiO.sub.2 /Al.sub.2 O.sub.3 are used as catalysts, preferably in bags. This patent does not disclose the use of any other catalysts, in particular oxides of higher molecular weight, or other chemical reactions.
According to DE-A-40 34 074, alkyl glycosides can be prepared in a reaction distillation column. In this case, the reaction is catalyzed homogeneously by liquid acids, and the catalyst is discharged with the reaction product. The alkylglycosides must therefore be neutralized by alkali after the reaction.
Thus, there remains a need for a method of carrying out a chemical reaction in a reaction distillation column which is free of the above-described drawbacks. In particular, there is a need for a method of carrying out a chemical reaction in a reaction distillation column which permits the use of catalysts which are stable at high temperatures and permits the easy replacement or removal of inactivated catalyst. There also remains a need for apparatus comprising a reaction distillation column which can be used in such a method.